Tag Archives: IBC

Minimum Design Loads and Risk

Minimum Design Loads and Risk

Model Building Codes, such as IBC (International Building Code), offer minimum design loads for climactic forces such as snow and wind. As building permit issuing agencies adopt codes, within their scope they can establish minimum values for their particular jurisdiction.

Key word here “minimum” – least values a building may be designed for and still obtain a permit to build.

I have long been an advocate for structural designs above minimum requirements. All too often potential new post frame building owners have not had adequate consultative design recommendations enough to find out increases in structural strength are often achieved with minimal investment.

For an earlier article concerning this subject please see https://www.hansenpolebuildings.com/2015/11/bike-helmets-and-minimum-building-design-loads/.

From IBC Section 1604.5, “Each building and structure shall be assigned a risk category in accordance with Table 1604.5. Where a referenced standard specifies an occupancy category, the risk category shall not be taken as lower than the occupancy category specified therein.”

Balance of IBC Chapter 16, including Table 1604.5 may be perused here: https://codes.iccsafe.org/public/document/IBC2018/chapter-16-structural-design.

Buildings representing a low hazard to human life in event of a failure include agricultural facilities. In most jurisdictions, detached garages and shops are also considered to be a fit and these would be considered as Risk Category I. In many areas agricultural buildings are either permit exempt, or do not have to go through structural plan reviews and inspections.  Read a very expensive story about an agricultural building using minimal requirements: https://www.sbcmag.info/content/9/design-load-reductions-risk.

Risk Category I buildings are designed to allow for an occurrence greater than minimum design loads of once in 25 years (or a 4% chance in any given year). In theory, all buildings in this category should collapse within 25 years of construction.

Sobering, isn’t it?

Shopping for a new post frame building and want yours to be last one standing when a storm of a century comes to visit? If so, I would hope whomever you are speaking with offers options of increasing Risk Category from I to II. And bumping up snow loads by 5, 10 or even more pounds per square foot and/or increasing design wind speed by a few more miles per hour.

If you are not offered these options – ask for them. I’d like to have your building be left standing!

Fiberglass Panels, Accurate Info, and Truss Bracing!

DEAR POLE BARN GURU: I have four skylights with old fiberglass panels that are in need of being replaced. I doubt the design of the panel can be matched easily but am wondering if I send you a piece of it if it can be. I understand the way to go is with a polycarbonate, not fiberglass, panel. Thanks DAVE in BAY

DEAR DAVE: As you are finding out, skylights are problematic. Here is some extended reading on why: https://www.hansenpolebuildings.com/2012/01/skylights/.

If indeed you determine the only solution is to replace fiberglass panels with polycarbonate (me, I would replace them with steel panels and be done with the future headache) I would recommend a visit to the ProDesk at your local The Home Depot® as they can order in most anything and it usually comes in freight free, which can prove to be a significant savings.

DEAR POLE BARN GURU: I am buying a building immediately but your website is too intrusive to shop, so I will not be using you. I, like many others, do not like the setup for quotes because in most cases you turn into used car salesmen. BRAD in KNOXVILLE

DEAR BRAD: Thank you very much for your input. In order to be able to provide accurate pricing and design advice to our clients, we do need to gather some basic information. Things like where is your new post frame building to be constructed (so we get the correct climactic loading conditions), as well as how do we best reach you to discuss your proposed project. We get several hundred new inquiries each day, seven days a week, and frankly you are the first to voice an opinion as to our website being intrusive. If you have constructive solutions as to how we can best glean the information needed to be able to best provide our services, without coming across as being ‘intrusive’ we would welcome your input, as we always strive to improve.

Our Building Designers are highly trained professionals whose mission is to assist our clients in the quest for the ideal dream building which melds imagination, budget and available space. Post frame buildings are highly involved, engineered structures, which ideally require a fair amount of interaction between us and the client to arrive at the best design solution. We do not “sell” anything to anyone – we provide the assistance to our clients, as well as the education which enables our clients to invest in The Ultimate Post Frame Building Experience™, should they decide we are the best fit. Most of our clients have spent hours perusing the thousand plus pages of free information on our website and have decided they are going to own a new Hansen Pole Building long before they ever request a quote.

 

DEAR POLE BARN GURU: Question about my plans. On the drawings, my purlin spacing is noted as 31” OC. On the truss drawing, I see that it says the bracing for the top chord is 24” OC. Am I reading this correctly? 

It states: 

(Switched from sheeted: Spacing > 2-0-0).

and then below it talks about the Bottom Chord: Rigid ceiling directly applied or 6-9-13 oc bracing. What does that mean?

Thanks! DAN in QUAKERTOWN

DEAR DAN: Truss drawings are designed without any knowledge of how a particular building is constructed, or what the final bracing system for the entire structure is – the permanent bracing design is left to the engineer of record (see General Safety Notes #2).

You will note the top chord bracing says 2-0-0 purlins then says the maximum spacing is 4-7-0 (least of the three drawings). The 31″ spacing on the plans is far less than the 55″ maximum.

Bottom chord bracing is a function of a maximum L/d (length divided by depth) ratio of L/80 for members in tension (truss bottom chords are in tension as they are preventing the walls of the building from going out). The width of a single 2x member is 1.5″ X 80 = 120″ maximum for a single width 2x member. You will note on the endwalls of the building there is a 2×4 nailed to the face of the bottom chord of the truss. This now makes the member three inches in width so technically it could be braced once every 240″ (or 20 feet). The same goes for the interior double trusses, the three inch width member is good up to 20 feet without being braced laterally.

 

 

Prohibition of Pole Barn Construction

The Construction of Pole Barns is Prohibited

Seriously?

This is directly from the White Bear Lake Township (Minnesota) ordinances related to Building Codes, buried deep in their Ordinance No. 8:

5-34. POLE BUILDINGS. The construction of pole barns/buildings is prohibited in the Town.

I found this as a result of an article in the White Bear Press, excerpted below:

“There was also a lengthy discussion regarding pole barns after Planner Tom Riedesel presented several amendments recommended by the Variance Board and Planning Commission.

It all started with a request from residents Don and Janice Stock on Portland Avenue to replace an existing pole barn with a new upgraded design post-frame building. Historically, pole barns have not been allowed by the township due to building quality and aesthetics. However, the quality has improved over the years, so the Board approved the variance with strict standards for construction. Don Stock, whose home is located in the far northeast section of the town, spoke at the meeting to assure the board that the building will match the brown on his home’s natural cedar siding.”

It was reassuring to see the Board approving the variance. Post frame (pole) buildings are Code conforming structures, in accordance with the IBC (International Building Code). It is acceptable for jurisdictions to legislate the exterior appearance of a structure (colors or types of exterior coverings), however it would be a restriction of trade to attempt to prohibit a building system.

I’ve successfully won similar discussions throughout the country – all it has ever taken is a phone call to discuss with the jurisdiction’s legal representation. Attorneys seem to have an understanding of what this type of prohibition truly means in respect to trying to defend against it. It is a no win.

Running into a similar circumstance with your new proposed post frame building? If so, please feel free to pass along the situation to me, chances are more than fair I can assist with its quick resolution.

Design Wind Speed Changes

Design Wind Speed Changes with Building Code Editions

Every three years a new version of the International Building Code (IBC) is printed, which brings with it the latest and greatest information for building design as approved by Code Officials. State and local permit issuing jurisdictions then can either adopt or amend the Code as they best see fit.

Even though the Code is updated on a three year cycle, some jurisdictions opt to continue to utilize earlier versions of the Code.

Provisions for design loads are set forth in Chapter 16 of the IBC.

There are significant changes to the design wind load requirements for fenestration between the 2009 IBC and the 2012 editions of the same code. These are due to significant changes to the wind load provision of ASCE (American Society® of Civil Engineers) 7 between the 2005 and 2010 edition.

The design wind load provisions of the 2005 and earlier editions of ASCE 7 were based upon allowable stress design of building components. The intent of this method was to provide loads to which the building components had a fairly high likelihood of being exposed during the service life of the building. The building components were then designed to remain serviceable (i.e. not require replacement) when subjected to this load.

The 2010 edition of ASCE 7 provides design wind load provisions which are based upon strength design of building components. This method provides loads which have a lower likelihood of occurring during the service life of the building. The building components are then designed not to fail (rupture) when subjected to this load.

This change in methodology results in higher design wind speeds and pressures. At first glance, this might give the appearance of requiring higher DP (Design Pressure) ratings. In actuality, the 2012 IBC contains provisions to multiply this new, higher load by a factor of 0.6 for the purpose of conversion to the more traditional method of determining the design wind pressure based upon allowable stress design. It is very important the builder, code official, manufacturer and anyone else involved in choosing or approving the structural building design for a particular application understand the higher design wind pressure provided by the 2012 IBC must be multiplied by this 0.6 conversion factor.

In most, but not all, cases this conversion results in required design pressure ratings which are roughly comparable to the more traditionally determined values.

ASCE7-10 also provides three different design wind speed maps. The different maps are based upon the assigned Risk Category of the building being designed.

  1. There is one map for buildings whose collapse would present a low risk to human life, such as barns and storage facilities.
  2. There is a second map for buildings whose collapse is considered to be a moderate hazard to human life. Most buildings fall within this category.
  3. There is a third map for buildings whose collapse is considered a high threat to human life, and for those which are considered essential facilities. The former includes assembly or education buildings designed to house groups of 250 or more people, some medical care facilities and any other buildings designed to house 5,000 people or more. Essential facilities include occupancies such as hospitals and police and fire stations, which are essential during emergency response situations.

The new maps result in higher design wind loads for buildings of moderate hazard to human life than for those of lower hazard. The highest design wind loads are given by the third map for buildings of high hazard to human life and essential facilities. Previous editions of ASCE 7 and the IBC also required these types of buildings to be designed to higher design loads, but the actual increase was applied in a different manner.

Considering a new post frame (pole) building? If you are looking at a building which is NOT designed by a registered design professional (RDP – engineer or architect) then there is an excellent chance the person or persons involved in the design do not understand the changes brought about by the newer editions of the Code and you could end up with an under designed building.

Under design can result in catastrophic failure – or even death. Don’t take the risk, demand an engineered building.

Your life or the lives of your loved ones could be at stake.

Proposed Building Code Change to Add to Construction Costs

During each 3-year-cycle of the International Building Code (IBC) and International Residential Code (IRC), there exists an opportunity to propose modifications and improve the codes to recognize new and innovative construction.  During the final two weeks in April, the code proposal hearings were held in Louisville, Kentucky where several hundred proposals were discussed and considered for inclusion in the code.

large-span-trusses-150x150While post-frame construction is typically used in agricultural applications which are often (and in my humble opinion sadly) considered exempt from code compliance, more and more post-frame construction is either residential housing (IRC) or commercial (IBC) in nature.  In these cases, changes which impact the code may have an effect on how post-frame buildings are constructed.

Eight proposals were identified by NFBA (National Frame Building Association) staff as having a potential impact on post-frame construction.  While the majority of these proposals were defeated, the following action should be noted:

S138-16: Submitted by the Structural Engineers Association, this proposal was approved and will require special inspection for wood trusses with a clear span of 60 feet or greater or an overall height of 60 inches or greater.  While the clear span is not a major issue, the 60 inch height may impact a number of projects creating new cost/scheduling issues.  This change is scheduled to be included in the 2018 IBC.

Having spent my entire adult life installing, designing, selling, building, delivering and purchasing wood trusses, it would seem ludicrous to require a special inspection for wood trusses with an overall height of 60 inches or greater. This would add an extra layer of inspection to nearly every building (not only post frame) project, with seemingly no apparent rationale other than the employment of a large number of people to perform these inspections (most likely the same structural engineers who made this proposal).

Trusses spanning 60 feet or more, are already required to have special inspections, under the IBC: https://www.hansenpolebuildings.com/2013/12/wide-span-trusses/.

What can you do? Contact your local Building Official today and ask them to vote to repeal this costly measure which does little or nothing to improve the safety of buildings.

Dear Pole Barn Guru: Why Didn’t You get the Snow Load Right?

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays.  With many questions to answer, please be patient to watch for yours to come up on a future Monday segment.  If you want a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU: I recently ordered a pole building kit package. The agreed snow load was 35. A minimum of 34 is required in our area. The calculations supplied are for 28, not 34. So now we are out another $800 and

back to square 2.

What can be done, and how fast? SNOWING IN SNOHOMISH

DEAR SNOWING: We’d all like to believe Building Department Plans Examiners are infallible. The reality is, the IBC (International Building Code) is a huge and complex document, which is further complicated by its references to numerous other outside documents.                  

The agreed upon snow load which you purchased, was 35 pounds per square foot (psf) as a GROUND SNOW LOAD (or Pg). The Code references a document called ASCE 7-10 (for the 2012 version of the Code). ASCE 7-10 gives the formula to convert Pg to flat roof snow load (Pf). This formula takes into account factors such as Building Importance, if Building is heated or not and the roof’s exposure to the wind. The roofing material also comes into play with the heating or not of the building.

 Pf is also adjusted for roof slope, to get to the design sloped roof snow load (Ps).

 In your particular case, our office made a call to your plans examiner who has now been happily educated.

 For further reading on this subject, please see the article I wrote for Structural Building Components magazine: https://sbcmag.info/article/2011/it-isnt-your-grandpas-barn-tips-technicians-designing-post-frame-trusses

DEAR POLE BARN GURU: I have an old metal barn that needs new doors and hardware. A pair of sliding doors that are each 10′ wide by 14′ tall. We had a storm that blew them off and damaged the tracks and channels. We live in Fowler, Colorado. Do you have a dealer here in Colorado? Or can we get them from you to install ourselves? Any information would be appreciated. CAUGHT IN COLORADO

 DEAR CAUGHT: Sliding doors can be a challenge in wind storms. If they are not correctly designed, installed, or kept closed and latched during high winds, they can all too easily end up as an unusable pile of rubbish. Sliding door frames which are built either partially or all from wood, are especially susceptible to failure under load.

 Hansen Pole Buildings provides sliding door systems and components direct to builders and end users in all 50 states. The doors are designed for the average individual to successfully assemble and install their own sliding doors, by following the detailed step-by-step instructions.

Call us and we will get you started on the path to replacing those doors.

DEAR POLE BARN GURU: Hello, I am helping a friend build and install sliding doors on his pole building. The building is otherwise complete. The door openings are pretty much ready to go as I can see. They are framed in and the upper track is installed. So here I come with a pile of steel siding, steel studs, track for SIDS and button of doors, rollers (pendant) and screws… The instructions he has are very vague. Can you provide me with any plans, prints, instructions of any kind please? Also a photo or diagram of what the finished product should look like?

They have a binder with instructions that supposedly came with the kit and your logo on the front of it. I’m not there at this time so if you need the model name/# I can send it to you this afternoon when I get there.  WONDERING IN WASHINGTON

DEAR WONDERING: While our sliding door systems are relatively simple for the average individual to install – having the detailed step-by-step instructions included in our Construction Guide, in hand would be a serious assist.

 The manual devotes 18 pages which include actual photos, as well as diagrams showing how to properly (as well as most quickly) assemble and install each component. Check the manual for these pages and then let me know if you still need help. Often people think the instructions come with the door and we’ve found having them in the Construction Guide makes them easier to find.

Use and Occupancy Group Classification Part II

As I said yesterday, in life, most everything is given some type classification whether it’s objective, such as motor vehicle operators’ licenses (automobile, commercial, motorcycle, etc.), or subjective, such as social status (wealthy, middle class, poor). Then there are those who are in “a class all by themselves.” My wife seems to think I fit in this category, which I take as a compliment! Buildings, like much of everything else, are classified, as well.  If you didn’t read yesterday’s blog – or if you did, review it quickly to get your head around the rest of the occupancy group discussion.

Yesterday I discussed “mixed group” classifications of buildings, such as fire stations and office buildings.

To continue, another occupancy group which relies on objective criteria is the High-Hazard Group H. Group H occupancies are assigned based on maximum quantities of materials which pose a physical or health hazard.

These materials may be used for manufacturing or processing, stored in the building, or generated as a product or byproduct through a process. Upon first glance, determining which H occupancy group is appropriate may seem to require a chemical engineering degree. However, material safety data sheets (MSDS) and the quantities involved allow for a practical guide. Discussing the project with a fire plans examiner at the building department can prove helpful as well.

Institutional (Group I) occupancies include buildings with occupants who are under supervised care, living in a controlled environment where they’re limited physically by either age or health, or they have personal liberties restricted by detention for penal or correctional purposes. Group I-3, which includes prisons, jails and correctional facilities, is further subdivided into “conditions.” However, unlike the occupancy subgroups, the five conditions are numbered with increasing risk to the higher numbers.

Residential (Group R) occupancies apply to buildings which are used for sleeping purposes, among the many other uses associated with residential uses. R-1 and R-2 groups apply to buildings which house occupants in large numbers. R-1 includes transient type housing consisting of hotels and motels, while R-2 housing is more of a permanent nature, such as apartments and dormitories. Groups R-3 and R-4 are required to comply with the requirements of the International Residential Code (IRC). R-3 occupancies include single detached houses and duplexes, and R-4 occupancies include assisted living and residential care facilities that have more than five, but less than 16, occupants, including staff.

Returning to mixed occupancies, designers of buildings involving multiple occupancies within the same structure have the option of selecting one of two types of mixed occupancies: Separated or non-separated uses. Mixed occupancies can be considered as “separated” because fire barriers of varying fire-resistance ratings are required between certain occupancies, or mixed occupancies can be non-separated, without any fire barriers.

There is a catch however, as the height and area requirements for each occupancy group used are to be applied to the entire building, and the most restrictive construction type will be applied to the entire building.

Allowable areas and building heights may be increased through consideration of automatic fire sprinkler protection and wide yards around the building.

Additionally, construction types are also of significant importance in properly applying the building code since they establish minimums based on building materials. The establishment of occupancy types is based on years of research and experience, and it is one of the essential building blocks in developing an effective building code.

And I can’t say this enough times…when in doubt take a trip to your friendly building department to discuss your building.  Take along a concise but complete list of all of the “uses” your new building will involve.  It will make your whole project slide along much smoother. These people want to see you build.  Their job is to ensure the health and safety of those using your new building.